1. Field of the Invention
The present invention relates to an elongated light-emitting device including an LED, an illuminating device using the elongated light-emitting device as a backlight, and a liquid crystal display including the illuminating device.
2. Description of the Related Art
Recently, display devices using a liquid crystal panel, which is thinner than a CRT (cathode ray tube), have been widely used. The liquid crystal panel, not emitting light itself, displays an image by using external light or by being irradiated with light from an illuminating device.
Examples of illuminating devices for use in liquid crystal displays include the sidelight type backlight proposed in JP-A-2004-21147 (pages 4 and 5, FIG. 1). This sidelight type backlight is used by being placed behind a liquid crystal panel, and is formed of a flat plate called a light guide plate formed of acrylic resin and a light-emitting device that is placed along a side surface of the light guide plate. The light-emitting device is formed of LEDs (light emitting diodes) arranged in line to serve as a light source. Light emitted from the light-emitting device is reflected inside the light guide plate to propagate through it; the light is then emitted from a light emitting surface formed on the front surface of the light guide plate to illuminate the liquid crystal panel.
A description will be given of a light-emitting device incorporated in a sidelight type backlight with reference to FIGS. 12 to 16. FIG. 12 is a diagram schematically showing the structure of a typical conventional light-emitting device. As shown in FIG. 12, a light-emitting device 140 has LEDs 143 arranged in line inside a reflector 142. A reflective material is formed on an inner surface of the reflector 142, and an opening is formed at a side of the reflector 142 at which the light emitting side of the LEDs 143 is located. As shown in FIG. 13, the LEDs 143 are arranged on a film 141 and connected in series to one another by a conductor 144 provided in the film 141. The conductor 144 is provided such that both ends thereof reach an end portion 141a that extends outward from the reflector 142 so as to be connected to an LED driver (not shown) that is provided outside the light emitting device 140. This film 141 is formed of two layers of films, and the conductor 144 is arranged between the two layers of films. The pattern of the conductor 144 and the region necessary for it is determined according to specifications for current capacity and voltage. Light emitted from the LEDs 143 directly enters a light guide plate (not shown), or enters the light guide plate after it is reflected at the inner surface of the reflector 142.
In the case where connection to the LED driver is achieved by using a wire harness or an FFC (flexible flat cable), instead of the end portion 141a extending outward from the reflector 142, a connector 145 as shown in FIG. 14 is provided so as to be connected to the conductor 144.
As shown in FIG. 15, in the case where a plurality of groups of LEDs are provided so as to lower the voltage to be applied, the LEDs in each group being connected in series to one another, both ends of the conductor 144 of each LED group connecting the LEDs therein need to be extended to the end portion 141a, and accordingly, a larger region is necessary. Furthermore, when a connector is provided, this region becomes even larger.
In the case where, as the LEDs 143, RGB-LEDs that are capable of emitting light of three colors of R (red), G (green), and B (blue), are used, three times larger amount of conductors are necessary compared with the case where an LED having one chip is used, because each one of the LEDs 143 is provided with terminals corresponding to the chips of the three colors and each of the terminals needs the conductor 144. FIG. 16 shows the film 141 used in the case where RGB-LEDs are used and two groups of LEDs that are connected in series to one another are provided. In this case, the region necessary for the conductor 144 increases, and it further increases if a connector is provided.
Today, thinner illuminating devices have been required to achieve thinner liquid crystal displays; in a sidelight type backlight, it is necessary to reduce the thickness of a light-emitting device provided along a side surface of a light guide plate. However, the height (“h” in FIG. 12) of the light-emitting device 140 is determined according to the region necessary for the conductor 144 in the film 141 and the region necessary to arrange the LEDs 143, and hence, the height of the light-emitting device 140 is increased as the pattern of the conductor 144 becomes more complicated and the conductor 144 requires a larger region.